Top drive drilling systems are well known in the art for drilling a wellbore for extracting subterranean natural resources from the earth. A top drive drilling system typically has a number of complex components including a top drive assembly supported by a derrick or drilling tower. A top drive assembly typically has a motor that rotates a main shaft that couples to a drill pipe for rotating a drill string (with a drill bit assembly) down a borehole. In some cases, the top drive assembly moves upwardly and downwardly on rails, or it can move via a cable/pulley system connected to the derrick. In either case, the top drive assembly is moved up and down about the derrick during drilling operations.
During drilling, the motor rotates the main shaft which, in turn, rotates the drill string and the drill bit assembly. Rotation of the drill bit produces the wellbore, often many miles into the earth. Drilling fluid (mud) is pumped into the top drive system and passes through an interior passage or conduit in the main shaft and through the drill string and to the drill bit assembly at the bottom of the wellbore.
In ordinary drilling operations of makeup of the top drive assembly to a drill pipe, the top drive assembly is hoisted up while pulling an unattached drill pipe for coupling to a stump (i.e., an upper end of a drill string in the earth). Once the unattached drill pipe is hoisted up and vertically oriented, a gripper device of the top drive assembly grips the female threaded end of the hoisted drill pipe. The top drive assembly rotates its main shaft (having a threaded pin/quill) clockwise for threadably mating the threaded pin of to the female end of the hoisted drill pipe while the gripper grips/positions the drill pipe. This is one “makeup” operation of the threaded pin to the drill pipe. With acme threads, for instance, about 2.5 inches of thread travel occurs during such makeup, which requires some amount of vertical travel of the top drive assembly in order to compensate for the thread travel as the threaded pin is threadably coupled to the drill pipe.
To compensate for such thread travel, existing systems utilize a simple spring configuration, whereby one or more springs are provided near the gripper assembly such that the spring(s) compress as the threads of threaded pin engage with the drill pipe. The spring(s) allow the top drive assembly to move vertically downward during threading, thereby compensating for the thread travel effectuated about the threaded pin and the drill pipe. The opposite holds true for breakout of the threaded pin from the drill pipe, whereby the spring(s) expand to compensate for thread travel during breakout operations (i.e., as the threaded pin is disengaged from drill pipe after the drill pipe has been drilled approximately 90 feet down with the drill string). Breakout is needed after the drill pipe has been drilled down a given distance so that the top drive assembly can hoist another drill pipe and repeat makeup operations.
However, such spring(s) are prone to failure because they often get clogged with mud and other debris because they are exposed to the environment. They are also unreliable and can fail due to the amount of force and torque exerted by the top drive assembly onto the drill pipe. The spring(s) configuration can delay or halt drilling operations, which is very costly and problematic. Also, the spring(s) can exert unnecessary vertical tension to threads during makeup and breakout operations of the top drive assembly to and from a drill pipe, which can shorten the life of drill pipes and their threads.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.